1. Field of the Invention
This invention relates generally to the field of oil well, gas well, water well and subterranean pollution remediation well equipment, and more particularly to a dual concentric half screen for filtering sand and undesirable solids from fluids, gases, and toxic extractions.
2. Brief Description of Prior Art
Many types of screens and filtering devices are known in the art that are designed to exclude sand and other solids from fluids and gases produced from oil, gas, water, and pollution remediation wells without undue restriction of the production rate of fluids or gases. These devices are sometimes used as the sole means of excluding solids, and are otherwise used with filter aids, such as gravel and/or sand, which are either incorporated within the device or are separately placed surrounding the device.
Wire wrapped screens, slotted liners, and perforated liners are examples of devices used inside a drilled hole. The drilled hole may be left open or may have a casing or liner cemented and perforated prior to positioning such a device. Openings in such screens and liners may be designed to stop, or bridge, undesirable solids contained in fluids. Screen and well liners are sometimes surrounded by filter aids. The filter aids consist commonly of gravel. When used with filter aids or gravel, the openings in the screens and liners are designed to stop or bridge the filter aid and the filter aid is designed to stop or bridge the undesirable solids contained in the produced fluids.
Prepacked screens, porous media filter devices and such, are examples of devices that incorporate a filter media in the screen body. These devices are used for the same purpose with and without additional filter aids in the well bore. These filter aids commonly consist of gravel.
Multiple wrap screens provide two or more concentric wire wrappings which act as multiple filters in one device to prevent invasion of undesirable solids and are used with or without additional filter aids in the well bore.
One problem that all of the prior art devices have in common is that they are subject to erosion by fluids or gases that flow through them and by the particles that are carried through them by the produced fluids and/or gases. Multiple wrapped screens, prepacked screens, and other screen devices that incorporate a filter aid as part of the body of the device, physically resist but often do not stop the effect of such erosion. Another common problem is that screens, liners, and especially prepacked screens are that they are all easily clogged or partially clogged by solids that fill the openings of the screens or fill the pores of the filter aids contained in the device, or surrounding device, thus reducing their capacity to transmit fluids or gases.
Another common problem is created when the fluid that carries the gravel easily flows into the screen as it is being pumped down the screen/casing, or screen/hole annulus. This reduces the velocity of the carrier fluid in the annulus, thereby increasing the gravel concentration and interfering with the transport of gravel over the entire screen length. This is especially a problem in high angle holes, deviating from the vertical by 45 degrees to 90 degrees plus, as gravity forces the gravel to the low side of the hole and forms "dunes" that interfere with subsequent movement of gravel down the annulus. As gravel accumulates, the carrier fluid is diverted to the high side of the well bore and into the screen, thereby reducing the velocity of the carrier fluid flowing in the outer annulus and the capability of the fluid to force gravel toward the bottom, or the end, of the screen.
Very long (100 to 2,000 plus feet), high angle (45 degrees to 90 degrees plus) well bores are especially difficult to pack with gravel because the gravel is preferentially deposited on the low side of the hole by gravity as the gravel is being pumped and after the pumping stops, the gravel tends to settle, leaving the top of the screen uncovered. Thereafter, the uncovered portion of the screen is subject to erosion by solids entrained in produced fluids and/or gases, and the screen openings are more readily clogged by the undesirable solids.
The problem with multiple concentric wire wrapped screens is that fluids, gases and solids entrained therein erode holes because there is little resistance to flow through the screens and because these holes do not provide any means of restricting bypassing of gravel carrier fluids from the screen/casing or screen/open hole annulus.
The art known in this field simply does not address all of these issues and problems. For example, Metler, U.S. Pat. No. 3,279,259, attempts to prevent this problem by providing a well screen assembly that is comprised of a plurality of concentric pipes. Each of the sleeves or pipes have perforations that are staggered in respect to the perforations in the next adjacent sleeve so that erosive fluid entering the well is forced to follow a tortuous flow path before it impinges on the tubing.
McLaughlin, et al., U.S. Pat. No. 1,594,788, shows a well screen that uses concentric tubes or sleeves. The slots or openings in the two sleeves have different shapes to prevent wear.
Thompson, U.S. Pat. No. 2,681,111, discloses a screen with perforations that are also staggered between adjacent sleeves.
Other relevant patents include Grubsbeck, et al., U.S. Pat. No. 4,046,198; Maly, et al., U.S. Pat. No. 3,637,010; Sparlin, U.S. Pat. No. 4,771,829; Van Westrum, U.S. Pat. No. 2,155,744; Burns, U.S. Pat. No. 2,942,664; Chancellor, et al., U.S. Pat. No. 3,153,451; Jones U.S. Pat. No. 3,428,128; and Gurley, et al, U.S. Pat. No. 3,789,927.